1. Field of the Invention
The present invention relates generally to soil remediation equipment and, particularly, without limitation, to such equipment utilizing a combustion chamber in a rotating drum.
2. Description of the Related Art
Remediation of contaminated soil is, and will continue to be for the foreseeable future, a large and growing industry. For example, soil containing hydrocarbons due to service station ground leakage must be cleaned or removed before the property can be transferred. Companies that have developed equipment and experience for similar applications, such as asphalt plant plants, are a natural for providing the skills and facilities needed for soil remediation.
The generally applied method of remediating contaminated soil is to heat the soil with a large combustion heater to a sufficiently elevated temperature, such as approximately 500.degree. F., in an inclined rotating drum, that gravitationally flows the soil continuously therethrough. The elevated temperature releases the contaminants--typically hydrocarbons, both short chain and long chain--from the soil by vaporization. The soil is then removed from the rotating drum and cooled for reuse.
The vapors, containing the contaminants and combustion products from the burner used to elevate the soil temperature, are usually directed, after filtering, into an afterburner. The afterburner generally comprises a second large burner that, in conjunction with the combustion properties of the contaminates, further elevate the temperature of the vapors in order to break down and oxidize contaminates remaining in the vapors. Short-chain or light hydrocarbons, such as those arising from service station leakage, vaporize at approximately 500.degree. F. and require afterburning at approximately 1600.degree. F.; long-chain or heavy hydrocarbons, such as those arising from coal gasification production, vaporize at approximately 1000.degree. F. and require afterburning at approximately 2,000.degree. F. The afterburned vapor, which is relatively clean, is cooled and/or filtered and exhausted into the atmosphere. Typically, such a described soil remediation system can treat 25 to 50 tons of contaminated soil per hour.
Similarly to long-chain hydrocarbon clean-up, clean-up of PCB contamination is more energy intensive than short-chain hydrocarbon cleanup.
One attempt to reduce energy consumption during soil remediation is disclosed in U.S. Pat. No. 5,170,726 wherein heat staging of soil contaminated with short-chain and long-chain hydrocarbons was utilized in an attempt to reduce the afterburning temperature to 1600.degree. F. Unfortunately, however, the system was more complex in that not one, but two, drums were required. Soil is heated by a first large burner to approximately 500.degree. F. in a first drum followed by cascading the heated soil into a second drum with a second large burner to further elevate the temperature of the soil and vapor to approximately 1000.degree. F. The vapors containing long-chain hydrocarbons that were released at the 1000.degree. F. of the high-temperature drum were then vented through the first large burner of the low-temperature drum to simultaneously afterburn the long-chain hydrocarbons during the first-stage heating of the contaminated soil in the first drum. Thus, in theory, the only hydrocarbons entering a separate afterburner were the short-chain hydrocarbons that were vaporized in the first drum. Unfortunately, energy consumption, although reduced, is still excessive.
What is needed is a soil remediation system that vaporizes and afterburns the volatilized contaminates--including short-chain hydrocarbons, long-chain hydrocarbons, and PCB's--with a single drum and a single burner to thereby substantially reduce energy consumption even further and to exhaust clean soil and clean vapor at a temperature of approximately 450.degree. F.